1. Field of the Invention
This invention relates generally to water jet pumps and propulsion units, and more particularly to a sliding-blade water jet propulsion apparatus suitable for use as a propulsion unit for jet propulsion watercraft.
2. Brief Description of the Prior Art
Various watercraft propulsion apparatus are known in the art. Modern screw propellers are highly efficient thruster units, however, the problem of cavitation limit their potential to increase the speed of the watercraft.
Water jet propulsion units utilizing pumps and external drives are also known in the art which, in principle, can accomplish fast travel on water. However, most of these types of propulsion assemblies are relatively complicated designs, have large overall dimensions, and have large energy losses associated with the conversion of fuel combustion energy into kinetic energy associated with the movement of the watercraft. There are several patents which disclose water jet propulsion units utilizing pumps and external drives.
Henmi, U.S. Pat. No. 5,277,631 discloses a vane arrangement for a water jet propulsion assembly.
Schulze, U.S. Pat. No. 5,366,396 discloses a water-jet drive with a stator and a rotor enclosed by a housing having an inlet and an outlet nozzle and has a torque transmitting means at one end of the rotor supporting shaft.
Gerard et al, U.S. Pat. No. 5,045,002 discloses a jet propulsion assembly for ships which includes an axial or semi-axial propeller type pump.
Cernier, U.S. Pat. No. 5,265,549 discloses a hydro-propelled ship with a pair of propulsion turbines affixed to a starboard side and a port side of the hull.
Propulsion apparatus wherein the gas expansion process is combined with the jet stream generation in the same operating chamber are also known in the art. The optimal value for velocity is equal to twice the watercraft cruising speed. An increase in propulsion efficiency can be accomplished by creating a jet stream of large mass with relatively low velocity. A classical single-circuit ramjet for watercraft has low propulsion efficiency because the ratio of it's cruise speed and the velocity of jet propulsion is far from the optimal value.
Krautkremer et al, U.S. Pat. No. 4,411,630 discloses a water jet drive mechanism for driving a watercraft which includes an elbow located in the hull which contains a pump by which water is sucked in through a suction passage and is ejected downwardly through an ejector passage. A gas is supplied to the water jet at the ejector passage.
The ejection and mixing type of propulsion units wherein the gas expansion process is combined with the jet stream generation have large hydrodynamic and thermal losses due to the enthalpy of converting the working gas into a high velocity head and mixing of the gas with water in the expansion process.
Pulsating hydro-jet engines wherein the gas expansion work is transmitted to the added mass of water by the use of a flat hydrodynamic piston which separates the gas expansion work from the jet stream generation overcome some of the problems of the ejection and mixing type units.
Jastram et al, U.S. Pat. No. 3,951,094 discloses a gas driven, pulsating water jet propulsive duct drive for watercraft which has a water inlet aperture at the front end with a closure member which opens and closes periodically and a gas power outlet behind the inlet aperture. The forward inlet of the water filled duct is periodically closed and the power gas power outlet opened to feed gas under pressure into the duct and expel the fluid.
Jarry, U.S. Pat. No. 3,872,665 discloses an underwater pulse jet motor comprising a stator and a rotor within the stator which has axially extending ducts at it's periphery. The stator includes a closing segment which closes off the forward ends of the ducts as they pass it during rotation of the rotor. Gas under pressure is injected into the ducts through a passage in the stator in alignment with the closing segment.
In reality, hydrodynamic and thermal losses will develop in the pulsating hydro-jet devices because the steep wave front caused by pulsation of the working medium will be broken and mixing of both masses will occur when the masses are interacting. It is also well known that pulsating propulsion has significant disadvantages compared to continuous flow propulsion.
The present invention overcomes these problems and limitations of the prior art.